Barcodes have been utilized for identifying and pricing objects for more than thirty years. Most typically, barcodes are used in retail to identify the item of merchandise. For example, a gallon of milk may contain a barcode that, when scanned, will notify the cashier of the price of the milk.
Yet in recent years, barcodes have acquired new purposes as computers and barcode scanners have become more portable. The circuitry required to scan a conventional one-dimensional barcode can now be housed in a device as small as a typical keychain. As a result, many mobile telephones, personal digital assistants (“PDAs”), and pagers can be retrofitted with or connected to a laser-based scanning device. This allows the mobile device to function as a scanner capable of storing hundreds or thousands of scanned barcodes.
Mobile devices with attached scanners have allowed for the development of a new niche in the wireless electronics business. Some companies have developed software and hardware which allows a user to scan any barcode and be redirected to media information (e.g., a website, product description, price, etc.) about the scanned product. These programs provide a link between the physical and online world which previously did not exist.
However, mobile devices with attached scanners possess some drawbacks which have curtailed their expansion into the mobile marketplace. First, there are few mobile devices produced for the general public that contain integrated laser-based scanners. Therefore, for a user to acquire scanning capability for a mobile device, he/she must purchase additional equipment. The additional scanning equipment also adds size and weight to the mobile device, thereby reducing its mobility.
Currently, many cell phones and mobile devices are available with built-in cameras. The explosion of the availability of affordable digital cameras and their inclusion into mobile devices is driven by several factors. One of the most important is the recent availability of inexpensive image sensors based on CMOS technology. The cameras on these devices provide a means for capturing the barcode information which was previously only accessible via a laser-based scanner. Decoding barcode images from digital cameras included in mobile devices presents several difficult problems. These problems go well beyond the challenges addressed in commercial barcode readers. Barcode decoding algorithms from commercial products will not consistently decode images from a consumer portable device. Some of these problems are addressed below:
Lighting:
Most mobile devices with integrated digital cameras do not have built-in flashes and rely solely on the ambient light for illumination. Using highly variable ambient light makes pattern recognition much more difficult. Shadows, shading across the length of a barcode, overexposure, underexposure, and similar problems that are typical of any camera not utilizing a flash can foil traditional barcode decoding algorithms that are designed for highly controlled lighting environments.
Size:
The distance between a digital camera and its target object is not usually rigidly controlled. This translates into a large range of possible sizes (magnifications) that a barcode can have on a fixed size image sensor.
Skew:
As any photographer knows, taking pictures at an angle changes the apparent shape of the object to a viewer. A barcode with a rectangular shape, when viewed straight-on, can look like a trapezoid (or irregular quadrilateral) when viewed from an angle. The location and addressing of image pixels for a barcode change dramatically when viewed from the side, or tilted. Algorithms to decode barcodes from digital images must be able to address images distorted from skewed viewing angles, but must do so within the constraints of limited hardware, processing power, and memory typically found in mobile devices such as PDAs and handsets.
Battery Power:
Portable devices run on batteries—the smaller the better. Barcode decoding algorithms for cameras must be very efficient so as to use low amounts of CPU power. Charge coupled diode (“CCD”) devices and barcode scanners using laser light generally require a large amount of power, and are not well suited for battery powered, handheld devices.
Color Imagers:
Consumer oriented devices such as mobile handsets generally are designed with color image sensors. However, barcode scanning typically operates best with gray-scale information. Color data typically requires three times the amount of storage and handling required by gray-scale. Data needs to be transferred through the camera's CPU and memory to be processed. For color imagers, specific image processing algorithms are required in order to avoid problematic image artifacts during the translation from color to grayscale.
Focus:
Digital cameras for portable devices are usually designed to work at a variety of distances. The need for a wider range of focus in cameras results in a trade off between the cost of the lens component and the sharpness of a typical image. Decoding algorithms for embedded digital cameras must be able to cope with a moderate degree of focus problems.
Low-Cost Lens Components:
In order to meet cost constraints of many portable device markets, manufacturers often compromise on the optical quality of camera lenses. This can present decoding technology with a different set of challenges from the simple focal length based focus problem noted above. Low-cost lens components can produce image distortions that are localized to a specific region or form a changing gradient across the image. This requires additional sophistication for decoding algorithms.
Limited Resolution:
The cost of a digital imaging CMOS sensor increases as the number of image pixels increases. Although the Asian market has seen the release of general purpose consumer devices like PDAs and cell phones with “megapixel” image resolution, it is unlikely these devices will be released in the mainstream European and North American markets in the near future. With fewer pixels to work with, it is significantly more difficult to reliably decode barcodes from images.
Based on the aforementioned described problems with mobile digital imaging, there clearly exists a need for a system capable of capturing, decoding, and analyzing barcode information obtained from a digital camera enabled mobile device. Such a system would enable the average mobile device user to accurately and reliably scan and decode any barcode available.